也许我完全错了，但我的目标是使用jquery、ajax和php来验证我的注册表。我目前已将其设置为：
用户在表单中输入数据
如果任何数据不正确，则使用ajax在表单下方显示一条错误消息
如果表单正确提交，数据将发送到数据库
几乎所有的事情看起来都很正常，但问题是如果表格填写正确，我会打电话给你

header("Location: ../index.php”);

然后它将我的索引页加载到register页的顶部，因为默认情况下不允许submit按钮将用户带到新页。就像我有两个网页在一个浏览器窗口上的一个。如果表格填写正确，我有没有办法“重新允许”提交按钮正常工作？
html格式：

<?php 
    include "shared/_header.php"; 
    include "shared/_navBar.php";
?>
<div class="wrapper-register">
    <div id="register-account">
        <div class="register-title">
            <h2>REGISTER ACCOUNT</h2>
        </div>
    <form action="shared/_registerAccount.php" method="post">
        <div class="register-input">
            <input id="register-username" type="text" name="username" maxlength="16" placeholder="Username" />
        </div>
        <div class="register-input">
            <input id="register-email" type="text" name="email" maxlength="128" placeholder="Email" />
        </div>
        <div class="register-input">
            <input id="register-password" type="password" name="password" maxlength="128" placeholder="Password" />
        </div>
        <div class="register-input">
            <input id="register-confirm-password" type="password" name="confirmPassword" maxlength="128" placeholder="Confirm Password" /> 
        </div> 
        <input id="register-submit" type="submit" name="submit" value="SIGN UP" class="register-button" /> 
    </form>
    <p class="form-message"></p>
</div>
</div>
    <?php include "shared/_footer.php" ?>
    <script src="javascript/register.js"></script>
</body>
</html>

jquery查询：

/// <reference path="jquery-3.3.1.min.js" />

$(document).ready(function() {

    $("form").submit(function(event) {

        event.preventDefault();

        var username = $("#register-username").val();
        var email = $("#register-email").val();
        var password = $("#register-password").val();
        var confirmPassword = $("#register-confirm-password").val();
        var submit = $("#register-submit").val();

        $(".form-message").load("../shared/_registerAccount.php", {

            username: username,
            email: email,
            password: password,
            confirmPassword: confirmPassword,
            submit: submit

          });
     });
});

PHP：

<?php

if (isset($_POST['submit']))
{
    include_once "_databaseHandler.php";

    $username = mysqli_real_escape_string($connection, $_POST['username']);
    $email = mysqli_real_escape_string($connection, $_POST['email']);
    $password = mysqli_real_escape_string($connection, $_POST['password']);
    $confirmPassword = mysqli_real_escape_string($connection, 
        $_POST['confirmPassword']);

    $errorEmpty = false;

    //Check for empty fields
    if (empty($username) || empty($email) || empty($password) || 
           empty($confirmPassword))
    {
        echo "<span class='form-error'>Please fill in all fields</span>";
        $errorEmpty = true;
    }

    else
    {
        $sqlUsername = "SELECT * FROM userinfo WHERE userName = '$username'";
        $resultUsername = mysqli_query($connection, $sqlUsername);
        $resultCheckUsername = mysqli_num_rows($resultUsername);

        $sqlEmail = "SELECT * FROM userinfo WHERE userEmail = '$email'";
        $resultEmail = mysqli_query($connection, $sqlEmail);
        $resultCheckEmail = mysqli_num_rows($resultEmail);

        //Check if username is taken
        if ($resultCheckUsername > 0)
        {
            echo "<span class='form-error'>This username is already 
                taken</span>";
            $errorEmpty = true;
        }

        //Check if username has invalid characters
        else if (preg_match("/^[0-9a-zA-Z]$/", $username))
        {
            echo "<span class='form-error'>This username contains invalid 
                characters</span>";
            $errorEmpty = true;
        }

        //Check if email is valid
        else if ($resultCheckEmail > 0)
        {
            echo "<span class='form-error'>This email is already in 
                use</span>";
            $errorEmpty = true;
        }

        //Check if email is already in use
        else if (!filter_var($email, FILTER_VALIDATE_EMAIL))
        {
            echo "<span class='form-error'>Please enter a valid email 
                address</span>";
            $errorEmpty = true;
        }

        //Check if passwords match
        else if ($_POST['password'] != $_POST['confirmPassword'])
        {
            echo "<span class='form-error'>Passwords do not match</span>";
            $errorEmpty = true;
        }

        //Insert the user into the database
        else
        {
            $sql = "INSERT INTO userinfo (userName, userEmail, userPassword) 
                VALUES (?, ?, ?);";

            $statement = mysqli_stmt_init($connection);

            if (!mysqli_stmt_prepare($statement, $sql))
            {
                echo "<span>Database error</span>";

                header("Location: ../index.php");
                exit();
            }

            else
            {
                $hashedPassword = password_hash($password, PASSWORD_DEFAULT);

                mysqli_stmt_bind_param($statement, "sss", $username, $email, 
                    $hashedPassword);

                mysqli_stmt_execute($statement);

                header("Location: ../index.php?signup=success");
                exit();
            }
        }
    }
}

else
{
    header('Location: ../index.php');
    exit();
}

?>

<script>

    $("#username, #email, #password, #confirmPassword").removeClass(".input- 
        error").removeClass(".input-error");

    var errorEmpty = "<?php echo $errorEmpty; ?>";

    if (errorEmpty)
    {
        $("#username, #email, #password, #confirmPassword").addClass(".input- 
            error");
    }

    if (!errorEmpty)
    {
        $("#username, #email, #password, #confirmPassword").val("");
    }

</script>